As can be
seen, its handling is easy. However, each solar chart serves only to a given
latitude, so we must learn to build our own solar chart. As it is a laborious
process, I will discuss it in two different entries.

The first
thing to know is that the stereographic solar chart is a representation of the
ecliptic, or sun path on a horizontal plane. However, the paths are directed to
a central point, instead of using an orthogonal projection. This singular
projection allows us to discern the sun path in the lower latitudes.

The first
step is to draw the Sun's path on a sphere in the days of the equinox. This
path corresponds to an arc, which is projected as a line on the sphere
representing the sky. Then we draw the solstice paths, which are also
circumference arcs, which are separated from the equinox by the tilt angle of
the axis of the Earth; 23.44º.

When drawing
circumference arcs equidistant from both solstices, we obtain the trajectories
of the Sun in each month.

The second
step is to project the position of the hours on the ecliptic equinox, knowing
that every hour is separated from the previous 15 degrees.

The third
step is to tilt the solar paths, according to the latitude where we are. Following
the example we consider latitude 40º. Accordingly, the ecliptic will be tilt
40º.

In this same
step we will project the ecliptic on the horizontal plane of the sphere. To do
this, the points that are on the plane are projected directly onto the ground,
while the points on the sphere will be directed to lower vertex. Thus, we draw
the sun path on the day of the equinox.

In the fourth
step, we operate in the same way with the trajectories of the solstices: the
points on the horizon are projected directly onto the ground, while the points
on the sphere are directed towards the lower vertex.

In the fifth
step, we operate in the same way with the rest of the year. Thus, we have sun
paths drawn every month for a latitude of 40 °.

In the next
post I will explain how to find the hours in solar paths. Soon.